Acid mine drainage (AMD) is a global environmental issue. Conventionally, a number of active and passive remediation approaches are applied to treat and manage AMD. Case studies on remediation approaches applied in actual mining sites such as lime neutralization, bioremediation, wetlands and permeable reactive barriers provide an outlook on actual long-term implications of AMD remediation. Hence, in spite of available remediation approaches, AMD treatment remains a challenge. The need for sustainable AMD treatment approaches has led to much focus on water reuse and resource recovery. This review underscores (i) characteristics and implication of AMD, (ii) remediation approaches in mining sites, (iii) alternative treatment technologies for water reuse, and (iv) resource recovery. Specifically, the role of membrane processes and alternative treatment technologies to produce water for reuse from AMD is highlighted. Although membrane processes are favorable for water reuse, they cannot achieve resource recovery, specifically selective valuable metal recovery. The approach of integrated membrane and conventional treatment processes are especially promising for attaining both water reuse and recovery of resources such as sulfuric acid, metals and rare earth elements. Overall, this review provides insights in establishing reuse and resource recovery as the holistic approach towards sustainable AMD treatment. Finally, integrated technologies that deserve in depth future exploration is highlighted.

Increased reactive nitrogen (N) loadings to terrestrial ecosystems are believed to have positive effects on ecosystem carbon (C) sequestration. Global “hot spots” of N deposition are often associated with currently or formerly high deposition of sulphur (S); C fluxes in these regions might therefore not be responding solely to N loading, and could be undergoing transient change as S inputs change. In a four-year, two-forest stand (mature Norway spruce and European beech) replicated field experiment involving acidity manipulation (sulphuric acid addition), N addition (NH4NO3) and combined treatments, we tested the extent to which altered soil solution acidity or/and soil N availability affected the concentration of soil dissolved organic carbon (DOC), soil respiration (Rs), microbial community characteristics (respiration, biomass, fungi and bacteria abundances) and enzyme activity. We demonstrated a large and consistent suppression of soil water DOC concentration driven by chemical changes associated with increased hydrogen ion concentrations under acid treatments, independent of forest type. Soil respiration was suppressed by sulphuric acid addition in the spruce forest, accompanied by reduced microbial biomass, increased fungal:bacterial ratios and increased C to N enzyme ratios. We did not observe equivalent effects of sulphuric acid treatments on Rs in the beech forest, where microbial activity appeared to be more tightly linked to N acquisition. The only changes in C cycling following N addition were increased C to N enzyme ratios, with no impact on C fluxes (either Rs or DOC). We conclude that C accumulation previously attributed solely to N deposition could be partly attributable to their simultaneous acidification.

This research aims to study the wet torrefaction (WT) and saccharification of sorghum distillery residue (SDR) towards hydrochar and bioethanol production. The experiments are designed by Box-Behnken design from response surface methodology where the operating conditions include sulfuric acid concentration (0, 0.01, and 0.02 M), amyloglucosidase concentration (36, 51, and 66 IU), and saccharification time (120, 180, and 240 min). Compared to conventional dry torrefaction, the hydrochar yield is between 13.24 and 14.73%, which is much lower than dry torrefaction biochar (yield >50%). The calorific value of the raw SDR is 17.15 MJ/kg, which is significantly enhanced to 22.36–23.37 MJ/kg after WT. When the sulfuric acid concentration increases from 0 to 0.02 M, the glucose concentration in the product increases from 5.59 g/L to 13.05 g/L. The prediction of analysis of variance suggests that the best combination to maximum glucose production is 0.02 M H₂SO₄, 66 IU enzyme concentration, and 120 min saccharification time, and the glucose concentration is 30.85 g/L. The maximum bioethanol concentration of 19.21 g/L is obtained, which is higher than those from wheat straw (18.1 g/L) and sweet sorghum residue (16.2 g/L). A large amount of SDR is generated in the kaoliang liquor production process, which may cause environmental problems if it is not appropriately treated. This study fulfills SDR valorization for hydrochar and bioenergy to lower environmental pollution and even achieve a circular economy.

Spiramycin is a widely used macrolide antibiotic and exists at high concentration in production wastewater. A thermal-acid hydrolytic pretreatment using silicotungstic acid (STA) under microwave (MW) irradiation was suggested to mitigate spiramycin from production wastewater. Positive correlations were observed between STA dosage, MW power, interaction time and the hydrolytic removal efficiencies, and an integrative equation was generalized quantitively. Rapid and complete removal 100 mg/L of spiramycin was achieved after 8 min of reaction with 1.0 g/L of STA under 200 W of MW irradiation, comparing to 30.1% by MW irradiation or 15.9% by STA alone. The synergetic effects of STA and MW irradiation were originated from the dissociated-proton catalysis by STA and the dipolar rotation heating effect of MW. STA performed much better than the mineral acid H2SO4 under MW, due to the much stronger Brönsted acidity and higher Hammett acidity. After 8 min, 98.0% of antibacterial potency was also reduced. The m/z 558.8614 fragment (P1) and m/z 448.1323 fragment (P2) were identified as the primary products, which were formed by breaking glucosidic bonds and losing mycarose and forosamine for P1 and further mycaminose moiety for P2. Finally, production wastewater with 433 mg/L of spiramycin was effectively treated using this thermal-acid hydrolytic method. Spiramycin and its antibacterial potency both dropped to 0 after 6 min. The potency drop was supposed from the losing of mycarose and/or forosamine. To decrease both the concentration of spiramycin and its antibacterial potency, combinedly using STA and MW was suggested in this work to break down the structural bonds of the functional groups rather than to destroy the whole antibiotic molecules. It is promising for pretreating spiramycin-contained production wastewater to mitigate both the antibiotic and its antibacterial potency.

The main objective of this study was to unravel the chemical reactions and processes dictating the potential bioavailability of vanadium (V). In environmental solutions V exists in two stable oxidation states, +IV and +V, of which + V is considered to be more toxic. In this study, the effect of speciation and soil pH on the chemical accessibility of V was investigated with two soils: 1) field soil rather rich in soil organic matter (SOM) and 2) coarse mineral soil low in SOM. Fresh soil samples treated with V(+V) (added as NaVO3) or V(+IV) (added as VOSO4) (pH adjusted to the range 4.0–6.9) were incubated for 3 months at 22 °C. The adsorption tendency of V species was explored by water extraction (Milli-Q water, 1:50 dw/V) and by sequential extraction (0.25 M KCl; 0.1 M KH2/K2HPO4; 0.1 M NaOH; 0.25 M H2SO4, 1:10 dw/V). The potential bioavailability of V was found to be dictated by soil properties. SOM reduced V(+V) to V(+IV) and acted as a sorbent for both species, which lowered the bioaccessibility of V. A high pH, in turn, favored the predominance of the V(+V) species and thus increased the chemical accessibility of V.

This study aimed to analyze the environmental impacts of the oxidative desulfurization (ODS) process catalyzed by metal-free reduced graphene oxide (rGO) through life cycle assessment (LCA). The environmental impacts study containing the rGO production process, the ODS process, the comparison of different oxidants and solvents was developed. This study was performed by using ReCiPe 2016 V1.03 Hierarchist midpoint as well as endpoint approach and SimaPro software. For the production of 1 kg rGO, the results showed that hydrochloric acid (washing), sulfuric acid (mixing), hydrazine (reduction) and electricity were four main contributors in this process, and this process showed a significant impact on human health 14.21 Pt followed by ecosystem 0.845 Pt and resources 0.164 Pt. For the production of 1 kg desulfurized oil (400 ppm), main environmental impacts were terrestrial ecotoxicity (43.256 kg 1,4-DCB), global warming (41.058 kg CO₂), human non-carcinogenic toxicity (19.570 kg 1,4-DCB) and fossil resource scarcity (13.178 kg oil), and the main contributors were electricity, diesel oil and acetonitrile. The whole ODS process also showed a greatest effect on human health. For two common oxidants hydrogen peroxide and oxygen used in ODS, hydrogen peroxide showed a greater impact than oxygen. On the other hand, for three common solvents employed in ODS, N-methyl-2-pyrrolidone had a more serious impact on human health followed by acetonitrile and N,N-dimethylformamide. As such, LCA results demonstrated the detailed environmental impacts originated from the catalytic ODS, hence elucidating systematic guidance for its future development toward practicality.

Bisphenol A, bisphenol S, and fluconazole are ubiquitous environmental pollutants and their removal from water is of utmost importance. As the biodegradation of these compounds is usually not enough effective, often other degradation methods are required. The study presents the difference between biodegradation and photo-Fenton degradation with a much higher efficiency obtained in the latter process. Levels of biodegradation and chemical degradation were assessed based on high-performance liquid chromatography determination. Optimization of the photo-Fenton removal of bisphenol A, bisphenol S, and fluconazole resulted in about 100 % primary degradation of both bisphenols during 10–20 min and almost 90 % primary degradation of fluconazole within an hour. Degradation products formed in the process were identified using liquid chromatography with mass spectrometry and showed central scission of bisphenol S with the formation of phenol and sulfuric acid while for bisphenol A and fluconazole the oxidation resulted in much smaller structural changes.

Soil and sludge are important pools for microplastics (MPs), however standard separation methods for MPs from these pools are still missing. We tested the widely used methods for MPs extraction from water and sediment to six agriculture surface soils and three sewage sludges from municipal wastewater treatment plants and included an additional pre-digestion procedure with 30% H₂O₂ before floatation to remove soil or sludge organic matter (OM). Extraction efficiency of MPs were evaluated under different separation conditions, including floatation solution (NaCl, ZnCl₂, and NaI), filtration membrane, and oxidation solution. Results showed that H₂O₂ pre-digestion significantly increased MPs extraction in soil and sludge, especially the samples with high OM contents, particularly sludge. Floatation solution with higher densities recovered more MPs. The extra released MPs were mainly small fibrous MPs, probably because they are easily retained by aggregates. Our results provide an feasible separation method for MPs in soil and sludge, i.e., pre-digestion with 30% H₂O₂ at 70 °C, floatation with NaI solution, filtration through nylon membrane, and further oxidation with 30% H₂O₂ + H₂SO₄ or 30% H₂O₂ at 70 °C. About 420–1290 MP items/kg soil were detected in soil samples, while much higher numbers (5553–13460 MP items/kg) were found in sludge samples. The dominate morphology of MPs was white fiber with a size of 0.02–0.25 mm, while the main types of MPs, identified by a micro-Fourier transformed infrared spectroscopy (μ-FTIR), were polyethylene and polypropylene in soil samples and polyethylene, polyethylene terephthalate, and polyacrylonitrile in sludge samples.

The catalytic hydrolysis of carbonyl sulfide (COS) and the effect of small clusters of H2O and H2SO4 have been studied by theoretical calculations. The addition of H2SO4 could increase the enthalpy change (ΔH<0) and decrease relative energy of products (relative energy<0), resulting in hydrolysis reaction changed from an endothermic reaction to an exothermic reaction. Further, H2SO4 decreases the energy barrier by 5.25 kcal/mol, and it enhances the catalytic hydrolysis through the hydrogen transfer effect. The (COS + H2SO4-H2O) reaction has the lowest energy barrier of 29.97 kcal/mol. Although an excess addition of H2O and H2SO4 increases the energy barrier, decreases the catalytic hydrolysis, which is consistent with experimental observations. The order of the energy barriers for the three reactions from low to high are as follows: COS + H2SO4-H2O < COS + H2O + H2SO4-H2O < COS + H2O+(H2SO4)2. Kinetic simulations show that the addition of H2SO4 can increase the reaction rate constants. Consequently, adding an appropriate amount of sulfuric acid promotes the catalytic hydrolysis of COS both kinetically and thermodynamically.

Sediments nearby harbors are dredged regularly, and the sediments require the stringent treatment to meet the regulations on reuse and mitigate the environmental burdens from toxic pollutants. In this study, FeCl₃ was chosen as an extraction agent to treat marine sediment co-contaminated with Cu, Zn, and total petroleum hydrocarbons (TPH). In chemical extraction process, the extraction efficiency of Cu and Zn by FeCl₃ was compared with the conventional one using inorganic acids (H₂SO₄ and HCl). Despite the satisfactory level for extraction of Cu (78.8%) and Zn (73.3%) by HCl (0.5 M) through proton-enhanced dissolution, one critical demerit, particularly acidified sediment, led to the unwanted loss of Al, Fe, and Mg by dissolution. Moreover, the vast amount of HCl required the huge amounts of neutralizing agents for the post-treatment of the sediment sample via the washing process. Despite a low concentration, extraction of Cu (70.1%) and Zn (69.4%) was done by using FeCl₃ (0.05 M) through proton-enhanced dissolution, ferric-organic matter complexation, and oxidative dissolution of sulfide minerals. Ferric iron (Fe³⁺) was reduced to ferrous iron (Fe²⁺) with sulfide (S²⁻) oxidation during FeCl₃ extraction. In consecutive chemical oxidations using hydrogen peroxide (H₂O₂) and persulfate (S₂O₈²⁻), the resultant ferrous iron was used to activate the oxidants to effectively degrade TPH. S₂O₈²⁻ using FeCl₃ solution (molar ratio of ferrous to S₂O₈²⁻ is 19.8–198.3) removed 42.6% of TPH, which was higher than that by H₂O₂ (molar ratio of ferrous to H₂O₂ is 1.2–6.1). All experimental findings suggest that ferric is effectively accommodated to an acid washing step for co-contaminated marine sediments, which leads to enhanced extraction, cost-effectiveness, and less environmental burden.